JPS596169B2 - Firing equipment for powder raw materials such as alumina - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for firing powdery raw materials such as alumina.

In this specification, the term "floating heat exchanger" is to be understood as including, for example, floating heat exchangers consisting of ducts and cyclones, as well as so-called auxiliary combustion furnaces equipped with burners.

Alumina is fired from a cake of aluminum hydroxide containing attached moisture (hereinafter referred to as cake), as shown below (1).
) drying, (2) dehydration, and (3) drying.

(1) Drying process: Cake→Al203・3H20+H20↑(2) Dehydration process: Al2O3・3H20→Al203・H20
+2H20↑Al203・H20→γ-Al203+
H20↑(3 firing process: γ-Al203→α-Al20
3. Figure 1 is a system diagram of a conventional alumina firing apparatus.

The raw material cake containing adhering moisture introduced from the middle of the duct 1 is dried before reaching the cyclone 2 and collected by the cyclone 2, and the collected raw material is introduced into the auxiliary combustion furnace 3. The raw material fed into the auxiliary combustion furnace 3 travels from a duct 4 to a cyclone 5, as shown by the solid line arrow, where it is dehydrated and collected. The raw material collected in the cyclone 5 is sent to a firing furnace 6 such as a rotary kiln.
and fired. The raw material fired in the firing furnace 6 is cooled in a primary cooler 7, further cooled in a secondary cooler 8, and discharged as a product from an arrow 9. However, the exhaust gas from the firing furnace 6 reaches the auxiliary combustion furnace 3 as shown by the broken line arrow, and also reaches the secondary cooler 8.
The high temperature air extracted from the duct passes through the duct 10 to the auxiliary furnace 3
The hot gas from the auxiliary combustion furnace 3 passes through the duct 4, the cyclone 5, the duct 1, the cyclone 2, the duct 11, the electrostatic precipitator 12, and is attracted by the induction fan 13. The auxiliary combustion furnace 3 and the firing furnace 6 are each equipped with a burner. Generally, the raw cake introduced through duct 1 has an attached moisture content of 13-14% and such a cake has to be dried between duct 1 and cyclone 2. Further, in order to prevent corrosion in the electrostatic precipitator 12, it is necessary to maintain the hot gas entering the electrostatic precipitator 12 at a temperature higher than the dew point. Moreover, increasing the temperature of the hot gas discharged from the cyclone 2 to an unnecessarily high temperature will lead to a decrease in heat consumption. Therefore, the temperature of the hot gas discharged from the cyclone 5 only needs to be about 450°C, for example. In order to make the temperature of the hot gas discharged from the cyclone 5 approximately 450°C, the temperature of the hot gas discharged from the auxiliary combustion furnace 3 to the duct 4 must be approximately 450°C. On the other hand, auxiliary combustion furnace 3
is in a mixed state of alumina raw material and hot combustion gas, and in order to achieve complete combustion in the auxiliary combustion furnace 3, at least the hot gas discharged from the auxiliary combustion furnace 3 to the duct 4 must be The temperature must be kept at 600°C or higher. If the temperature of the hot gas discharged from the auxiliary combustion furnace 3 to the duct 4 is set to about 450° C. as described above, a large amount of unburned matter will come out in the auxiliary combustion furnace 3, making it impossible to perform complete combustion in the auxiliary combustion furnace 3. In other words, Cyclone 5
The temperature of the hot gas discharged into the duct 1 is set at around 450°C, which is necessary for drying the raw material cake and maintaining the temperature above the dew point in the electrostatic precipitator 12, thereby improving heat consumption. However, on the other hand, complete combustion in the auxiliary combustion furnace 3 becomes difficult, a large amount of unburned matter is discharged, and heat consumption is reduced. Conversely, when complete combustion is achieved in the auxiliary combustion furnace 3, the temperature of the hot gas discharged from the auxiliary combustion furnace 3 into the duct 4 and the temperature of the hot gas discharged from the Cytalon 2 into the duct 11 rise. This results in poor heat consumption and a large amount of wasted heat being dissipated into the atmosphere. FIG. 2 is a system diagram of another conventional alumina firing apparatus that solves the problems of the prior art shown in FIG.

The alumina firing apparatus shown in FIG. 2 is partially similar to that shown in FIG. 1, and corresponding parts are designated by the same reference numerals and will not be described further. This prior art performs complete combustion in the auxiliary combustion furnace 3, so that the temperature of the hot gas discharged from the auxiliary combustion furnace 3 into the duct 4 is, for example, about 600°C, and furthermore, it suppresses wasted heat from being dissipated into the atmosphere. This is a device designed to do this.
The hot gas discharged from the auxiliary combustion furnace 3 is transferred to a duct 4, a cyclone 5, a duct 14, a cyclone 15, as shown by the broken line arrow.
It passes through the duct 16 and joins the hot gas from the hot stove 17 to reach the dryer 18. The raw material cake is put into the dryer 18, and as shown by the solid arrow, the dryer 18 passes through the duct 1.
While passing through 9 and reaching cyclone 20, the raw material cake is dried by hot gas. The dried and collected raw materials are introduced into the duct 14 from the cyclone 20 and collected by the cyclone 15. A dehydration reaction of the raw material occurs between the duct 14 and the cyclone 15, and the temperature of this dehydration reaction is about 350°C. Therefore, the temperature of the hot gas discharged from the cyclone 15 into the duct 16 is at most 350°C.
Stay in. Therefore, in this prior art, the dryer 1
The hot air stove 17 is required to bring the temperature of the hot gas discharged from the hot air heater 8 to about 450°C. Therefore, equipment costs become high. This hot air stove 17 is provided with a burner, and therefore, the operation for adjusting the combustion amount with the burners provided in the auxiliary combustion furnace 3 and the firing furnace 6, respectively, becomes complicated. Furthermore, since the hot-blast stove 17 has a limited heat resistance, the hot-blast stove 17 requires dilution air, resulting in poor heat consumption. The present invention solves the above-mentioned problems of the prior art, and embodiments will be described in detail below.

FIG. 3 is a system diagram of one embodiment of the present invention. Dryer 2
The alumina raw material cake is put into dryer 2.
Hot gas is introduced into 2 from a duct 23, and the cake and hot gas are led to a cyclone 25 from a duct 24. The raw material cake is transferred to dryer 22 and duct 2 as shown by the solid line arrow.
4 and then to the cyclone 25 where it is dried. The raw material collected by the cyclone 25 is introduced into the duct 26 and collected by the cyclone 27. The raw material collected by the cyclone 27 is charged into an auxiliary combustion furnace 28. The raw material introduced into the auxiliary combustion furnace 28 passes through a duct 29 to reach a cyclone 30, where it is collected. The raw material is in the duct 26, cyclone 27, auxiliary combustion furnace 28, duct 2
9. While reaching the cyclone 30, a dehydration reaction takes place.
The raw material collected by the cyclone 30 is charged into a firing furnace 31 such as a rotary kiln, and a firing reaction is performed in the firing furnace 31. The firing raw material discharged from a cover 32 provided on the discharge side of the firing furnace 31 is cooled by a primary cooler 33. In the primary cooler 33,
The raw material from the cover 32 is introduced into a duct 34 and collected by a cyclone 35. The raw material cooled in the primary cooler 33 is further cooled in the secondary cooler 36. In the secondary cooler 36, the raw material collected by the cyclone 35 is introduced into a duct 37,
It is collected as shown by arrow 39 and becomes a product. Room temperature air as cooling air is introduced into ducts 34 and 37 of the primary cooler 33 and the secondary cooler 36, respectively.
High-temperature air discharged from the cyclone 35 in the primary cooler 33 is introduced into the cover 32 on the discharge side of the firing furnace 31 through a duct 41, and is used as secondary combustion air for the burner 40 of the rotary kiln 31.
Hot gas from the firing furnace 31 is guided to the auxiliary combustion furnace 28. Room temperature air for cooling introduced into the duct 37 of the secondary cooler 36 passes from the duct 37 to the cyclone 38 to the duct 42.
is derived. Bleed air discharged from the duct 42 is led to the auxiliary combustion furnace 28 through the duct 43, and is used as secondary air for combustion in the burner 44 provided in the auxiliary combustion furnace 28. The hot gas discharged from the auxiliary combustion furnace 28 passes through a duct 29, a cyclone 30, a duct 26, and a cyclone 27, and is led from a duct 45 to the duct 23. Also, this duct 23
At this time, a part of the high temperature air extracted from the secondary cooler 36 and guided to the duct 42 is branched from the duct 46, merged in the duct 23, and guided to the dryer 22.
The hot gas discharged from the dryer 22 passes through the duct 24 and the cyclone 25, is guided from the duct 47 to the electrostatic precipitator 48, and is dissipated into the atmosphere via the induction fan 49. The dryer 22 is for drying the raw material cake while dispersing and suspending it in hot gas and sending it in a parallel flow. FIG. 4 is a graph showing the temperature dependence of the ignition loss of the dried raw material. Referring to this graph, it can be seen that the dehydration reaction of the raw material occurs rapidly at about 300 to 350°C. Therefore, when the raw material collected by the cyclone 25 is charged into the duct 26 and dehydrated by following the path of the auxiliary combustion furnace 28, the duct 29, and the cyclone 30, due to the complete combustion of the burner 44 in the auxiliary combustion furnace 28, When the temperature of the hot gas discharged from the auxiliary combustion furnace 28 to the duct 29 is, for example, about 600°C, in this embodiment, the temperature of the hot gas discharged from the cyclone 27 to the discharge duct 45 is, for example, about 300 to 350°C. Become. Therefore, at this temperature, it is difficult to dry the moisture adhering to the cake in the dryer 22, but according to the present invention, the high temperature air extracted from the secondary cooler 36 through the duct 42 (the temperature of this high temperature air is, for example, Approximately 60
00C) from the duct 46 to the duct 23 and led to the dryer 22.
The temperature of the hot gas discharged from can be adjusted to, for example, approximately 450°C. Therefore, (1) dryer 22
, the duct 24, and the cyclone 25. (2) The hot gas from the duct 47 to the electrostatic precipitator 48 can be dried at a dew point (for example, about 150 to 1
(60° C.) or higher to prevent corrosion of the electrostatic precipitator 48, and (3) to prevent the temperature of hot gas flowing from the cyclone 25 to the duct 47 from becoming unnecessarily high and worsening heat consumption. The hot air from the secondary cooler 36 bled by the duct 42 is directed to the auxiliary furnace 28 and also to the dryer 22, so that the flow rate of hot gas in that duct 42 and therefore the secondary cooler 36 is The amount of air extracted from the tank is relatively large.

Therefore, there is an advantage that the amount of heat recovered from the fired alumina product introduced into the duct 37 is increased. Note that the ducts 42, 43, 46 may be provided with dampers 53, 54, 55 for controlling the flow rate of high-temperature air.

FIG. 5 is an overall system diagram of another embodiment of the present invention, and parts corresponding to those of the embodiment shown in FIG.

A noteworthy feature is that in this embodiment, the dryer 22 shown in the third figure is omitted, and the high temperature air extracted from the secondary cooler 36 by the duct 42 is branched to the duct 46 and is discharged from the cyclone 27. Combined with hot gas, duct 50
This is to lead to the following. The raw material cake is duct 5
The waste is introduced from the middle of the water, passes through the duct 50, and is collected by the cyclone 25, where it is dried. In this embodiment as well, the temperature of the hot gas completely combusted in the auxiliary combustion furnace 28 and discharged into the duct 29 is, for example, about 600° C. or higher, and the raw material undergoes a dehydration reaction while reaching the cyclone 30, the duct 26, and the duct 27. . Therefore, the temperature of the hot gas discharged from the cyclone 27 into the duct 51 is, for example, about 30
Although the temperature is 0 to 350°C, since the high temperature air extracted from the secondary cooler 36 is joined from the duct 46 to the duct 50, the temperature of the joined hot gas is, for example, about 450°C. The temperature of the hot gas for drying the fuel cake introduced into the duct 50 can therefore be adjusted to an optimal temperature of about 450° C., for example. FIG. 6 is an overall system diagram of still another embodiment of the present invention, and corresponding parts of the embodiments of FIGS. 3 and 5 are given the same reference numerals.

In this embodiment, the auxiliary combustion furnace 28 in FIGS.
is omitted, and the hot gas from the firing furnace 31 is passed through the duct 5.
2 to Cyclone 30 led to cloudy weather. The raw material collected by the cyclone 27 is introduced into the duct 52. In addition to the cooler equipped with the primary cooler 33 and the secondary cooler 36 as described above, the present invention may be implemented in connection with a multi-stage cooler equipped with one cooler or with three or more coolers. .

As described above, according to the present invention, the high temperature air extracted from the cooler and the hot gas from the floating heat exchanger are combined and guided to the drying device for drying the raw material cake, so the floating heat exchange Even if the raw material undergoes a dehydration reaction in the dryer and the temperature of the hot gas discharged from the floating heat exchanger becomes undesirably low, high-temperature air extracted from the cooler is introduced and mixed, and the hot gas is introduced into the drying device. can be maintained at an appropriate temperature. Therefore, unlike the prior art described above, a hot air stove is not required, the equipment cost is low, and the heat consumption is improved because dilution air for the hot air stove is not required. In addition, since hot gas at an appropriate temperature is introduced into the drying device, unnecessary high-temperature hot gas is prevented from being dissipated into the atmosphere.
Good heat consumption.

[Brief explanation of the drawing]

Figure 1 is a system diagram of the prior art of the present invention, Figure 2 is a system diagram of another prior art of the present invention, Figure 3 is a system diagram of an embodiment of the present invention, and Figure 4 is the strength of the alumina raw material. A graph showing the temperature dependence of heat loss, FIG. 5 is a system diagram of another embodiment of the present invention, and FIG. 6 is a system diagram of still another embodiment of the present invention. 22...Dryer, 25, 27, 30...
... cyclone, 28 ... auxiliary combustion furnace, 31 ...
...Kilning furnace, 33...Primary cooler, 36...
...Secondary cooler, 48...Electric precipitator, 4
9...Suction fan.

Claims (1)

[Claims] 1 Equipped with a drying device for drying raw materials, one or more stages of floating heat exchangers, a firing furnace, and a cooler for cooling with cooling air, exhaust gas from the firing furnace is transferred to the floating heat exchanger. In the calcination apparatus for a powder raw material such as alumina, the drying raw material is guided from the floating heat exchanger to the cooler through the firing furnace, and the drying equipment is supplied with air extracted from the cooler. A calcination apparatus for a powder raw material such as alumina, characterized in that the temperature of the gas introduced into the drying apparatus is adjusted to a predetermined temperature by introducing the dried air and exhaust gas from the calcination furnace.